Because their faces were concealed, knights carried shields with special colors and emblems—and wore similar designs on their helmets, tunic, and horse trappings—so they could be recognized in battle and in tournaments. Such designs became known as a "coat of arms" because the knight used his personal design to decorate the tunic (called a surcoat) worn over his armor. The arts of heraldry developed from this practical beginning. The rules of heraldry were very strict. A knight could carry only one coat of arms, which was passed on to his eldest son when he died. Other children used their father's arms with some changes.